1. Field of the Invention
The invention relates to a magnetic field sensing module, a measurement method for measuring an external magnetic field, and a manufacturing method of a magnetic field sensing module.
2. Description of Related Art
As the portable electronic devices become popular, the technology of electronic compasses capable of sensing the geomagnetic direction becomes more and more important. When the electronic compasses are used in portable electronic devices having a compact size (e.g. smart phones), it is preferred that the electronic compasses are capable of tri-axial sensing in addition to meeting the size requirement. This is because the user may hold the cell phone tilted when hand-holding the phone, and a variety of holding angles are all possible.
To achieve tri-axial sensing, a conventional technology is to use the tilted wafer technology, which etches a silicon substrate to form a tilted surface and then forms a giant magnetoresistance (GMR) multi-film structure or tunneling magnetoresistance (TMR) multi-film structure on the tilted surface. However, depositing a thin film on the tilted surface may easily result in an uneven thickness of the thin film, and the etching process performed on the thin film is more difficult and hard to control the yield rate.
Another conventional technology is to use a composite sensing element to achieve tri-axial sensing. Specifically speaking, two GMR multi-film structures (or TMR structures) disposed to be perpendicular to each other and a Hall element are used for tri-axial sensing. However, since the sensitivity of the Hall element differs from the sensitivity of the GMR or TMR multi-film structures, the accuracy of one of the axes may be different from the accuracies of the other two axes. In this way, when the user rotates the electronic device to a different angle, the sensitivity to the same magnetic field may differ, and the trouble in use is thus caused.
In the conventional technology, two or more manufacturing processes are commonly used to achieve multi-axial sensing of the magnetic field. Namely, the manufacturing processes using two or more wafers to manufacture a multi-axial magnetic field sensing module, which complicate the manufacture process and make it difficult to reduce the manufacturing cost.